Community Corner

Is West Nile Virus in San Mateo County?

Find out where it's been found and what you can do about it.

Summer doesn't bring many reasons for complaint, but among the chief pests of the season is the mosquito, and not just for the itchy bites they leave behind.

West Nile virus is a mosquito-borne disease that originated in Africa. According to the San Mateo County Mosquito and Vector Control District, West Nile arrived via mosquito in the United States in 1999 and made its way to California by 2003.

Data updated on July 26 by the California Department of Public Health shows that so far in the state this year there have been four human West Nile virus cases along with 323 infected dead birds, 555 mosquito pools and positive tests on 27 sentinel chickens and four squirrels. 

Almost all West Nile figures are down from this time last year, with 173 fewer dead birds, 38 fewer mosquito samples, and three fewer human cases.

Just this week, the Santa Clara County Vector Control District announced that mosquitoes tested positive for West Nile virus in East San Jose. County employees sprayed a foggy mist from trucks on streets in the Berryessa area of San Jose on Friday to try to keep the virus from spreading.

It has previously been found in South San Jose, extending west to Saratoga and Cupertino.

Farther north in San Mateo County, two dead birds found in the city of San Mateo tested positive for the virus in early June. Multiple birds and squirrels were found to be infected in San Mateo County in 2012.

Although West Nile cases are down this year in California, some scientists fear the worst for coming years. David Dausey, a professor of public health at Mercyhurst University in Erie, Pennsylvania, told USA Today last summer that "climate change means warmer winters, milder springs and hotter summers, all of which 'create a longer season for mosquitoes to breed and ideal conditions for them to survive.'"

While West Nile virus can be deadly on rare occasion, USA Today reported that 70 to 80 percent of infected people never know they have it. But about 20 percent of people with the virus get a fever, headache, body aches, nausea, vomiting, and a skin rash that can last from a few days to a few weeks. According to the San Mateo County Mosquito and Vector Control District, about one in 150 cases results in "high fever, headache, neck stiffness, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness, and paralysis."

The best thing anyone can do to prevent West Nile virus in Menlo Park is to get rid of standing water, where mosquitoes breed and grow. Here are several key ways to do so at home:

  • Turn over buckets and other containers
  • Check your sprinkler system for leaks
  • Use mosquitofish in backyard fish ponds or stagnant pools that are breeding mosquitoes
  • Fix broken pipes
  • Use a sump pump to remove standing water from under your home
You should also tell the county immediately if you find a dead bird or squirrel on your property or in public, so they can test it for West Nile virus. 

San Mateo County also provides mosquitofish for free to any resident to put in backyard ponds, to help reduce the mosquito population. For more information on getting mosquitofish, click here.

Got any more mosquito or West Nile tips? Tell us in the comments!


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